Patent GB-756784-A (GB)
Title: Fluid and mechanical coupling with centrifugal and frictional clutches
IPC: F16D47/02
Filed: 1954-05-04
Abstract: 756,784. Clutches. DOMAN HELICOPTERS, Inc. May 4, 1954 [May 14, 1953], No. 12967-54. Class 80(2) [Also in Group XXIX] A coupling for use between the engine crankshaft 10 and the rotor (not shown), of a helicopter comprises a fluid coupling with an impeller 17 and turbine 19 and' has the impeller connected through a centrifugally operated positive clutch 55 to a driven member 25 and the turbine connected thereto through a hydraulically operated friction clutch 24. The engine crankshaft 10 drives through a flexible coupling 16 to a hollow shaft 15 secured to the impeller 17. The turbine 19 is rotatable on bearings 31 &c., and fast with a sleeve 30 carrying friction shoes 32 which can be moved radially outwards to engage a drum 24 by a plunger 33. The inner end of the plunger 33 carries a roller 38 engaging a cone 36 moved axially of the coupling by a rod 39. The rod is biased to the left of the Figure for engagement of the friction clutch by a spring 42, and is disengaged when the pressure of oil, admitted through a conduit 45 in the engine crankshaft, moves a piston 40 to the right in the cylinder formed by the shaft 15. The piston is formed with axial and circumferential grooves 49, 48 co-operating with a port 46 in the shaft 15 closed by a valve consisting of an axially slidable sleeve 47 surrounding the shaft and biased to the right of the Figure by a spring 50; the axial position of the valve sleeve is determined by a roller 53 on a lever 52 engaging a flange on the sleeve. Oil under pressure is supplied continuously to the cylinder and piston when the engine is running, so,that when the port 46 is closed, the piston 40 and the cone 36 are moved to the right from the position shown and the friction clutch is disengaged. When the valve sleeve 47 is allowed to move to the right under the influence of its biasing spring 50, the port 46 is opened and oil bleeds out through the grooves 48, 49, &c., to return to the engine sump. Accordingly the cone 36, &c., is moved back to the left by the spring 42 and the friction clutch is engaged. The driven drum 24 of the friction clutch is splined at 26 to the driven member 25 which is centred relatively to the drum by a tubular extension 28 axially slidable within the cone 36, the arrangement being such that the driven member can move axially relatively to the drum. The centrifugal positive clutch consists of radially movable pawls 55, on the face of the clutch drum 26, able, when the parts are rotated at sufficient speed, to move out against the inwardly directed force of springs 56 to engage notches 58 in the impeller casing. Engagement of the pawls 55 with the notches 58 is prevented, until the parts are rotating a synchronously, by a blocker ring 60. To operate the device, the helicopter engine is started with the friction clutch 24 disengaged, so that drag in the coupling does not start to drive the helicopter rotor. The friction clutch 24 is then engaged and the rotor is driven through the fluid coupling until it has accelerated to, say 100 r.p.m., the fluid coupling meanwhile slipping. When the engine and the rotor have reached substantially equal speeds as indicated by tachometers, the engine throttle is chopped to slow down the engine crankshaft relatively to the rotor and secure relative rotation between the pawls 55 and the blocker ring 60, and the positive clutch then engages to connect the crankshaft 10 directly to the driven member 25. To bring the rotor to rest, the engine is throttled down and the friction clutch 24 disengaged, the centrifugally operated clutch disengaging automatically.